Formation of optical element of light emitting device for improving light emitting rate

The present invention relates to a light emitting device in general, more particularly to a light emitting device having an improved light extraction rate.

FIG. 1 is a conventional semiconductor light emitting device 100, which is composed of a substrate 20, a multilayer structure 26, and an uppermost layer 24. As the semiconductor light emitting device 100, for example, a light emitting diode (LED) or a semiconductor laser can be considered. LEDs are pn junction devices designed to convert the input flow of electrical energy into the output flow of electromagnetic radiation. LEDs can emit electromagnetic radiation in the ultraviolet, visible, and infrared regions of the electromagnetic spectrum. Visible LEDs are typically used for lighting and displays, and also have applications as information links between electronic devices and their users. Infrared LEDs are useful in optisolators and fiber optic communications. Semiconductor lasers are made in the same way as LEDs.

The multilayer structure 26 includes, but is not limited to, a lower sealing layer 21, an upper sealing layer 23, and an active layer 22 in which photons are emitted. The upper sealing layer 23 may include the uppermost layer 24. When the semiconductor light emitting device 100 does not have the separated uppermost layer 24, the upper sealing layer 23 becomes the uppermost layer.

The sealing layers 21 and 23 and the active layer 22 of the multilayer structure 26 are usually formed of a III-V semiconductor, a III-nitride semiconductor, and an II-VI semiconductor. The top layer 24 can be epitaxially grown on the top sealing layer 23, which is also usually a III-V semiconductor, a III-nitride semiconductor, a II-VI semiconductor, or a compound thereof. However, the uppermost layer 24 may be a semiconductor compound different from the material forming the sealing layer 21 or the sealing layer 23. It is desirable that the uppermost layer 24 is made of a material having a band gap larger than that of the active layer 22 so as to be transparent to the light emitted by the active layer 22. The term "transparent" as used herein refers to an optical element transmitting light at a radiation wavelength of a particular semiconductor light emitting device, with less than about 50%, more preferably less than about 10%, single light path loss due to absorption or scattering. Means to do. The uppermost layer 24 can be a transparent substrate (super straight) wafer-bonded to the upper sealing layer 23. The uppermost layer 24 may also be a substrate on which an epitaxial layer is grown.

The lower sealing layer 21 and the upper sealing layer 23 are electrically connected to the active layer 22 and to the contacts 31 and 32. Usually, one sealing layer is doped with a donor to form an n-type sealing layer, and the other sealing layer is doped with an acceptor to form a p-type sealing layer. Therefore, when an appropriate voltage is applied between the contacts 31 and 32, the electrons from the n-type sealing layer and the holes from the p-type sealing layer are bonded in the active layer 22 to emit light isotropically. Emit. For a more detailed description of the semiconductor light emitting device 100 as an LED, see US Pat. No. 6,133, entitled "AlGaIn N-based LED Having Thick Epitaxial Layer for Improved Light Extraction" given to Michael R. Krames et al. No. 589, Fred A. Reference can be made to US Pat. Nos. 5,793,062 and 6,015,719, both entitled "Transparent Substrate Light Emitting Diode with Directed Light Output," granted to Kish, Jr. et al. .. All of these patents are incorporated herein by reference.

The semiconductor light emitting device 100 can be an LED 100. The problem with LEDs is the low efficiency of light extraction. It is said that the reason why the light extraction efficiency is low is that the light emitted from the LED 100 is only a small amount of the light energy emitted by the active layer 22 (for example, in the case of an AlGaAs LED having a transparent substrate, it is about 30%). That is. As a result of low light extraction efficiency, only a small portion of the electrical input consumed contributes to externally observable light. Light extraction efficiency is defined as the ratio of the number of photons emitted from an LED to the number of photons produced by the LED.

Path 3 in FIG. 1 shows the direction of photons emitted from the point light source 27 of the active layer 22. As shown by path 3, the absorption properties of contacts 31 and 32 contribute to the low light extraction rate. Photons traveling along the path 3 are reflected by the inner surface of the LED 100 and absorbed by the contact 31. The contacts 31 and 32 can be formed from metals such as gold, nickel, aluminum, titanium, chromium, palladium, and alloys or compounds thereof.

The mechanism of loss that causes low light extraction efficiency is absorption in the semiconductor light emitting device, reflection loss when light enters another material with a different refractive index, and absorption in the light emitting device. Includes total internal reflection. However, total reflection is the photon emitted by the active layer 22 reached at an angle greater than the critical angle (.theta.c) to the boundary of the light emitting device 100 and the surrounding material Yellow Sea, photons exiting from the semiconductor light emitting element 100 Prevent things. The critical angle (indicated by θc in FIG. 1) related to this embodiment is θc = arccine (n)_surrounding/ N_led) Defined by. Here, n_surroundingAnd n_ledIndicates the material surrounding the light emitting device and the refractive index of the light emitting device, respectively. LEDs are often encapsulated in epoxy, but their index of refraction (n)_epoxy) Is about 1.5. An LED made of one of the above-mentioned III-V semiconductor materials has a refractive index in the range of about 2.4 to about 4.1. Average refractive index (n)_led) Is about 3.5, and the typical value of θc is about 25 °. Therefore, among the photons emitted from the point light source 27 in the active layer 22, those that pass through an arbitrary surface in the "take-out cone" having a half-width of 25 ° are radiated from the LED to the outside. Photons that hit the interface between the LED 100 and the outer material of the extraction cone are repeatedly subject to total internal reflection and are absorbed, for example, by the semiconductor layer (including the active layer 22) or the contacts 31 and 32. That is, many photons that hit the surface at an angle greater than 25 ° with respect to the axis perpendicular to the surface are not radiated from the LED to the outside in the first stage. There is a need for LEDs with high light extraction efficiency, from which more of the emitted photons are extracted.

<p num="0009"> INDUSTRIAL APPLICABILITY The present invention is used to improve the light extraction rate of a semiconductor light emitting device and to guide, focus, and scatter light in order to obtain a desired radiation pattern. In the present invention, a semiconductor light emitting device adapted to fit one or more optical elements such as a Fresnel lens and a holographic diffuser, and the surface of the semiconductor light emitting element are stamped to form an optical element. The method is included. One or more surfaces of the semiconductor light emitting device 100 can be formed on a Fresnel lens or a holographic diffuser. The Fresnel lens allows more photons emitted from the active layer 22 to hit the surface of the semiconductor light emitting device 100 at an incident angle close to vertical, and can minimize the loss of light due to total reflection, so that the surface can be Fresnel. It is desirable to use a lens. Further, the surface of the semiconductor light emitting device formed on the Fresnel lens reduces the light reflection loss usually caused by the material of the lens having a refractive index different from the material constituting the semiconductor light emitting device. One or both of Fresnel lenses and holographic diffusers related to lithography techniques including, but not limited to, photolithography, electron beam lithography, ion beam lithography, X-ray lithography, holographic lithography, etc. It can be formed by etching. Chemical wet etching or dry etching techniques such as plasma etching, reactive ion etching (RIE), and ion beam etching (CAIBE) with the aid of chemical means can be used. Alternatively, ion beam shaving (ion beam)</p><p num="0010"> Stamping is another method of forming an optical element on the surface of a light emitting device. The stamping process is the ductile transition of the semiconductor material to be stamped. It is executed at a temperature higher than point). In one embodiment, stamping is integrated with the wafer bonding process. Since the wafer bonding process is usually carried out at around 600 ° C. or higher, the wafer bonding process can be easily integrated with the wafer bonding process, thereby improving production efficiency. In the wafer bonding process, the first absorbent substrate used as a template for growing an epitaxial layer of the desired quality is removed, and a transparent substrate is used to improve the light extraction rate. Accompanied by replacing with. As an option, at the time of bonding the transparent substrate to the first surface of the semiconductor light emitting device 100, a stamping block having a shape or pattern opposite to the desired optical element shape or pattern is provided in the second semiconductor light emitting device 100. It may be pressed against the surface of the surface, the surface of the transparent semiconductor, or both. When the pressure is released, a light emitting device with a surface shaped into the desired optical element is formed. Stamping blocks used for stamping typically have a melting point higher than the process temperature applied during the formation of optical elements. Suitable materials for stamping blocks include, but are not limited to, molybdenum alloys, graphite, silicon carbide, and sapphire. An optical element can be formed on one or more surfaces of a semiconductor light emitting device. The stamping process is an independent process, but it can also be done before, after, or at the same time as the wafer bonding process. Alternatively, the stamping process may be used to stamp the material that will later be bonded to the semiconductor light emitting device 100.</p><p num="0011"> The present invention can be easily adapted to fit different applications. For example, an optical element can be made to collimate light for illumination, or it can be made to focus light on an optical fiber. Further, any surface of the LED can be formed into one or more optical elements, and two or more surfaces can be formed into one or more Fresnel lenses. Reflective coatings can also be used to direct the collimated or focused light in the desired direction. A diode array formed by forming a large number of optical elements on the semiconductor light emitting device 100 can also be used for high output application purposes.</p><p num="0012"> Increasing the proportion of photons emitted towards a predetermined portion of the optical element further enhances the usefulness of the present invention. For example, even if a Fresnel lens is present, the photons that reach its edges are less beneficial, so a more confined-constricted radiation spot (confined-) that emits a larger proportion of the photons toward the center of the Fresnel lens. emission spot) LED can be made. Methods of confining photon radiation to selected regions of the active layer include ion injection or diffusion, oxide passivation, selective area growth, and selective area bonding. included. Alternatively, the outer edge of the semiconductor light emitting device 100 or the active layer 22 may be removed by etching. By removing the outer edges by etching, a light emitting device with sloping sides can be made.</p>

<figref num="1">It is the schematic of the conventional semiconductor light emitting element.</figref><figref num="2A">FIG. 5 is a plan view of a Fresnel lens in which grooves of different heights are provided at uniform intervals, which are designed to converge light.</figref><figref num="2B">It is a figure which showed the cross section of the convergent lens and the Fresnel lens of FIG. 2A.</figref><figref num="3A">FIG. 5 is a plan view of a Fresnel lens in which grooves of different heights are provided at uniform intervals, which are designed to diverge light.</figref><figref num="3B">It is a figure which showed the cross section of the divergence lens and the Fresnel lens of FIG. 3A.</figref><figref num="4A">It is a top view of a convergent Fresnel lens which has grooves of uniform height, and the distance between grooves is a function of the distance from the lens center.</figref><figref num="4B">It is a figure which showed the cross section of the convergent lens and the Fresnel lens of FIG. 4A.</figref><figref num="5A">FIG. 5 is a plan view of a divergent Fresnel lens having grooves of uniform height and using the distance between the grooves as a function of the distance from the center of the lens.</figref><figref num="5B">It is a figure which showed the cross section of the divergence lens and the Fresnel lens of FIG. 5A.</figref><figref num="6">FIG. 5 is a plan view of a Fresnel lens having grooves that are not concentric with respect to the center of the lens.</figref><figref num="7A">It is the schematic of the light emitting device which formed the Fresnel lens which collimates light on one taking-out surface based on this invention.</figref><figref num="7B">It is the schematic of the light emitting device which formed the Fresnel lens which focuses light on the extraction surface based on this invention.</figref><figref num="7C">It is the schematic of the light emitting device which formed the Fresnel lens which radiates light on the extraction surface based on this invention.</figref><figref num="8A">FIG. 6 is a schematic representation of a light emitting device whose surface is shaped into an optical element.</figref><figref num="8B">It is a top view of the surface of the holographic diffuser which can be used in this invention.</figref><figref num="9">It is the schematic which showed the typical example which integrated the stamping process and the wafer bonding process.</figref><figref num="10">It is a schematic diagram of an LED having an inclined side surface which formed a Fresnel lens on the surface.</figref><figref num="11">It is the schematic of the Fresnel lens formed on the restricted radiation spot LED which formed the natural oxide with anisotropy.</figref><figref num="12">It is a schematic diagram of a light emitting device in which a Fresnel lens that collimates light is formed on two opposing surfaces of a semiconductor light emitting element, and one of which is coated with a reflective material.</figref><figref num="13">It is a schematic diagram of a light emitting device in which a Fresnel lens is formed on two opposing surfaces of a semiconductor light emitting element, and a lens coated with a reflective material focuses light on an active layer.</figref><figref num="14">It is a schematic diagram of the Fresnel lens which focuses the light formed on the surface which is not the extraction surface of the semiconductor light emitting element in order to increase the intensity along the axis.</figref><figref num="15">FIG. 5 is a schematic view of a Fresnel lens that emits light and is formed on a surface other than the extraction surface of a semiconductor light emitting element and coated with a reflective material.</figref><figref num="16">It is the schematic of the light emitting device of a flip chip structure.</figref><figref num="17">It is a schematic diagram of a light emitting device having an active layer substantially perpendicular to a Fresnel lens.</figref><figref num="18">It is a schematic diagram of a diode array on a single substrate.</figref><figref num="19">It is the schematic of the display device which incorporated the light emitting device based on this invention.</figref>

The drawings referenced herein are not drawn to scale.

As used herein, the "extraction surface" refers to the surface of a light emitting device intended to be an optical output surface. The light emitting device can also include two or more extraction surfaces. For the sake of simplicity, the take-out surface is the top surface in the figure. The light emitting device can be an LED. The portion of the LED described here that produces light is the normal active layer of the LED. The "light emitting device" used here includes a device having at least one semiconductor light emitting device 100. The present invention includes both stamping the surface of the light emitting device into an optical element and forming a Fresnel lens or holographic diffuser on the surface of the light emitting device using any method including stamping. The present invention also includes a holographic diffuser formed on the surface of the light emitting device, but in this example and description, Fresnel lenses are mainly referred to for easy reference. For the same easy-to-understand example, the semiconductor light emitting device 100 will be described as a light emitting diode 100. Elements with the same sign in different figures are the same.

As shown in FIGS. 2A, 2B, 3A, 3B, 4A, 4B, 5A, 5B, the Fresnel lens 28 is on the surface as opposed to the single curved surface of the condensing lens. A series of concentric grooves are formed and constructed. Groove 1 has a curved or angled surface that acts as a refracting surface. Grooves 1 can be spaced at regular intervals, as shown in FIGS. 2A and 3A. As shown in FIGS. 2B and 3B, when the grooves of the Fresnel lens 28 are at regular intervals, the height of the grooves can be changed so that the Fresnel lens 28 has a desired focal length. The shape of the groove can be changed, for example, as shown in FIG. 2B to focus the light beam or as shown in FIG. 3B to diverge the light beam. Alternatively, when the grooves of the Fresnel lens 28 have the same height as shown in FIGS. 4B and 5B, the distance between the grooves 1 can be adjusted to obtain the Fresnel lens 28 having a desired focal length. In the Fresnel lens 28 shown in FIGS. 4A and 5A, the groove spacing becomes narrower as it approaches the edge of the lens. 4B and 5B show that the shape of groove 1 can be adjusted to guide the light as desired. The Fresnel lens of FIG. 4B focuses the light beam and the Fresnel lens of FIG. 5B diverges the light beam. Grooves 1 of the Fresnel lens 28 do not need to be placed concentrically around the center of the lens. For example, FIG. 6 shows a Fresnel lens 28 with non-concentric grooves 1. Fresnel lenses can be based on aspherical surfaces or spherical surfaces. Furthermore, the surface on which the Fresnel lens is formed does not have to be flat. Fresnel lenses can also be formed on any shaped LED, such as on a rectangular LED, on an elliptical LED, on a pyramid LED, and on a cylindrical LED. When forming the Fresnel lens 28 on a semiconductor light emitting device, optionally, a high groove near the edge of the Fresnel lens 28 in FIGS. 2B and 3B, and near the edge of the Fresnel lens 28 in FIGS. 4B and 5B.

2B, 3B, 4B, and 5B compare the thickness of the normal convergent or divergent lens 2 with the Fresnel lens 28. As shown, the Fresnel lens 28 is thinner than a normal lens 2 having substantially the same focal length. Fresnel lenses 28, which are thinner than ordinary thick lenses, are preferred for LED applications because the lens material (ie, the semiconductor material) inherently absorbs some light.

FIG. 7A illustrates a light emitting device having an optical element 28 formed on the surface, shown as a Fresnel lens 28. The Fresnel lens 28 formed on the extraction surface of the semiconductor light emitting device 100 assists the extraction of light from the semiconductor light emitting element 100, but this is radiated when the extraction surface is not flat and has a groove 1. This is because more photons hit the extraction surface at an incident angle close to vertical. Photons that hit the surface at an incident angle close to vertical are not totally reflected and are therefore easier to extract. Coating the bottom surface with the reflector 40 helps reduce light loss due to reflection or absorption loss on the bottom surface. Photons traveling along path 5 also undergo attenuation and final absorption. As will be described later, a Fresnel lens provided on the bottom surface can also be used to take out photons traveling along the path 5.

7A, 7B, and 7C illustrate how the radiation pattern of the light emitting device is manipulated by the distance δ, as well as the height of the Fresnel lens 28, the groove spacing, and the focal length. The distance δ indicates the distance between the active layer 22 and the Fresnel lens 28. The distance δ, the horizontal position of the Fresnel lens 28, and the focal length of the Fresnel lens 28 affect the light emission pattern of the light emitting device. When the light source is placed substantially close to the focal length of the condensing lens, the outgoing rays are substantially parallel, as shown in FIG. 7A. By changing the distance δ, the light beam can be substantially converged as shown in FIG. 7B or diverged as shown in FIG. 7C. Examples of converging light as shown in FIG. 7B can be used for applications to optical fibers.

There are many ways to form a Fresnel lens or holographic diffuser on the surface. The "engraving method" first forms the uppermost layer 24 on the multilayer structure 26, and then chemically wet etching or dry etching such as plasma etching, reactive ion etching, or ion beam etching (CAIBE) using chemical means. It is necessary to form a desired pattern on the uppermost layer 24 by an etching technique. As an option, a lithography technique can be used as the etching technique. Lithography techniques include, but are not limited to, photolithography, electron beam lithography, ion beam lithography, X-ray lithography, and holographic lithography. In addition, the surface is imprinted using ion beam shaving or focused ion beam shaving, the surface is ablated using scanned electrons or laser beams, and the surface is processed by discharge processing (EDM), or A desired optical element can be mechanically formed on the surface of the semiconductor light emitting element 100 by performing a shaving process or a scribing process.

Fresnel lenses or holographic diffusers can also be formed using a bonding method. In the bonding method, it is necessary to bond the optical element to the multilayer structure 26 using a usual bonding material. The bonding material can be deposited using common deposition techniques such as spinning, sputtering, vapor deposition, chemical vapor deposition, metal / organic chemical vapor deposition, gas phase epitaxial, liquid phase epitaxial, and molecular beam epitaxial. Although the bonding material is not shown in the embodiment shown in FIG. 7A, the bonding material is at the boundary 25a between the optical element 28 and the upper conductive layer 23. However, if the light emitting device includes a top layer 24, the bonding material may be between the optical element 28 and the top layer 24.

When the bonding method is used, the bonding material is n in order to minimize the reflected light loss at the boundary 25a or 25b._ledOr n_lens(N_ledAnd n_lensRefractive index (n) very close to (when is different)_bonding) Is desirable (Fig. 7A). In order to minimize the strain when the device is subjected to a temperature change, a bonding material having a thermal expansion coefficient equivalent to that of both the semiconductor light emitting device and the Fresnel lens 28 can be used. Further, the bonding material can be made transparent to the wavelength of light emitted by the active layer 22. For example, the lens and bonding material can be one of (but not limited to): high refractive index optical glass, GaP (600 nm, n to 3.3). ) III-V semiconductors such as InGaP (600 nm, n-3.7), GaAs (500 nm, n-3.4), GaN (500 nm, n-2.4), ZnS (500 nm, n-2.4). 2.4), ZnSe (500 nm, n to 2.6), CdS (500 nm, n to 2.6), CdTe (500 nm, n to 2.7), ZnTe (500 nm, n to 3.). II-VI semiconductors such as 1), Group IV semiconductors, and compounds such as Si (500 nm, n to 3.5) and Ge (500 nm, n to 4.1), high refractive index organic semiconductors, refractive index. High rates of organic compounds, and mixtures or alloys thereof. n_bondingIs n_ledAnd n_lensIf it is different from the above, reflected light loss occurs at both the boundary between the semiconductor light emitting device and the bonding material and the boundary between the bonding material and the Fresnel lens 28.

It is preferable to select a lens material that is bonded by pressing the lens and the multilayer structure in a high temperature environment without a bonding material. If no bonding material is used, the refractive index of the bonding material is n._ledIt is possible to reduce the increased light loss due to the difference from. Adhesion is described in more detail in US Patent Application No. 09/660,317 entitled "LED with Improved Light Extraction Efficiency", the content of which is incorporated herein by reference.

Yet another method that can be used in the present invention is the stamping method. FIG. 8A shows a light emitting device including the semiconductor light emitting element 100 and a surface on which the optical element 28 is formed. FIG. 8B shows a schematic view of a holographic diffuser that can be used as the optical element 28 of FIG. 8A. The surface of the holographic diffuser contains a large number of random, aperiodic microlenslets. The holographic diffuser diverges light and removes noise and color diffraction. FIG. 8B shows the optical element 28 as a holographic diffuser, which may be any other optical element, such as a normal lens, a Fresnel lens, or a reflector.

In the typical process illustrated in FIG. 9, the top layer 24 is stamped by a stamping block 70 that has a pattern opposite to that of the optical element 28. FIG. 9 shows a Fresnel lens 28 as the optical element 28. This stamping method can be used to form the optical lens 28 on any surface of the semiconductor light emitting device 100. Although FIG. 9 shows a wafer bonding process performed at the same time as stamping, it is understood that stamping can also be performed before or after wafer bonding, or as a completely separate and independent process. Let's go. For example, the optical element may be stamped on the semiconductor light emitting device 100 that is not wafer-bonded. Alternatively, the optical element can be stamped first on the material and then the material can be bonded to the semiconductor light emitting device 100.

In the stamping method, since the Fresnel lens 28 is formed on the uppermost layer 24 of the LED, it is highly probable that the refractive index of the Fresnel lens 28 and the refractive index of the uppermost layer 24 of the LED are the same. In the stamping process, the semiconductor light emitting device 100 is subjected to at least the ductile transition of the uppermost layer 24. Heat to point) and press the stamping block 70. If desired, a pressure of 100 psi or higher may be applied to facilitate stamping (the exact pressure depends on the material used and the process temperature). After stamping on the uppermost layer 24 of the semiconductor light emitting device 100, the pressure can be released and the temperature can be lowered in order to easily separate the stamping block 70 from the obtained light emitting device. In order to stamp an accurate Fresnel lens pattern on the semiconductor light emitting device 100, the material of the stamping block must be able to withstand the applied temperature and pressure. Therefore, it is appropriate that the material of the stamping block has a ductile transition point higher than the ductile transition point of the material (for example, a semiconductor material) whose surface is stamped. Examples of suitable materials for stamping blocks include molybdenum alloys such as TZM (a compound of molybdenum, titanium, zircon, and carbon), graphite, silicon carbide, and sapphire, stainless steel, Hastalloy , Kovar , Includes Nichrome , tungsten and tungsten alloys, tantalum, niobium, titanium alloys and the like.

Unlike the bonding process, which is usually a separate step in the manufacturing process, stamping can be performed at the same time as the wafer bonding (see FIG. 9), or before or after the wafer bonding process. The purpose of the wafer bonding process is to first remove the first substrate 20.1, which normally absorbs light, and then replace it with a new substrate 20.2, which allows more light to reach the outside. Is to improve the withdrawal rate of. The first substrate 20.1 is a material suitable for producing a semiconductor light emitting layer having desired mechanical properties. For example, standard absorbent substrate materials can be utilized to achieve high quality epitaxial growth and ensure lattice alignment. These absorbable growth substrates usually have a bandgap that is less than or equal to the radiant energy of the semiconductor light emitting device. After growing the multilayer structure 26, the first substrate 20.1 is removed. The first substrate 20.1 can be removed by methods including, but not limited to, chemical etching and wrap finishing / polishing.

After removing the first substrate 20.1, the optically transparent second substrate 20.2 is subsequently bonded to the semiconductor light emitting device 100. The bonding procedure involves heating the new substrate 20.2 to a temperature between 25 ° C and 1000 ° C, depending on its composition. For the wafer bonding process, see Fred A. It is explained in more detail in US Pat. No. 5,502,316 entitled "Wafer Bonding of Light Emitting Diode Layers" granted to Kish et al., The contents of which are incorporated herein by reference. By simultaneously pressing both the new substrate 20.2 and the stamping block 70 onto the semiconductor light emitting device 100, the stamping process can be incorporated into the wafer bonding process. The stamping block 70 can press the Fresnel lens 28 against the new substrate 20.2, the top layer 24, or both. Although only one optical element is shown in FIG. 9 for clarity and simplicity, the stamping block 70 may include patterns of two or more optical elements.

FIG. 10 shows a semiconductor light emitting device 100 whose side surface is inclined. When the side surface is tilted, the light extraction rate is improved by setting the angle at which photons are reflected, as shown as the difference between the path 3 and the path 4. When the sides are tilted, the photons emitted by the active layer 22 can travel along path 4 (solid line) instead of path 3. The path 3 is a path in the semiconductor light emitting device whose side surface is not inclined (see FIG. 7A). The path 3 shown by the dotted line in FIG. 10 shows that the photons emitted from the point 27 of the active layer 22 are reflected by the side surface and absorbed by the contact 31 when the side surface is not inclined. However, the path 4 shown by the solid line in FIG. 10 shows that the photons emitted from the light source 27 in the same direction in the inclined light emitting device are reflected in the direction of the Fresnel lens 28 and taken out from the light emitting device. .. Tilt the sides in this way to improve the efficiency of light extraction by directing some of the photons that cannot be extracted from the light emitting device to the extraction surface if not tilted. If the inclined side surface is coated with a reflective material 40 such as metal (for example, silver) or a dielectric to further reduce absorption, the light extraction rate is further improved.

FIG. 11 shows a light emitting device including a semiconductor light emitting device 100 in which the cross-sectional region of the active layer 22 is smaller than the cross-sectional region of the Fresnel lens 28. Here, the cross-sectional region is in a plane parallel to the boundary between different layers of the semiconductor light emitting device 100. An opening or protective ring can be used to block current from the edges of the active layer. Alternatively, ion injection or diffusion can be used to block the current from the edge of the active layer 22 or to allow the current to flow away from the edge. Selective area growth and selective area bonding, also called patterned wafer bonding and patterned epitaxial growth, are two yet alternative methods for confining light radiation. Selective region growth and selective region bonding are discussed in US Pat. No. 5,793,062, the contents of which are incorporated herein by reference. Further, by forming an oxide on the edge of the active layer 22 and inactivating it, a restricted-emission spot (confined-emission) is formed. spot) LED can be made. The restricted radiation spot LED, one of which is shown in FIG. 11, can be made using the Holonyak process. In the holoniac process, it is necessary to form the mesa 33 by keeping the LED at a temperature between 375 ° C and 550 ° C for up to 3 hours. The holoniac process is carried out to prevent the formation of unwanted aluminum oxide, in which an electrically insulating natural oxide 34 is formed above the limiting layer 23. For more information on the Holonyak process and its applications, see US Pat. No. 5,262,360 entitled "AlGaAs Native Oxide" granted to Nick Holonyak, Jr. et al. And Nick Holonyak, Jr. et al. US Pat. No. 5,517,039 entitled "Semiconductor Devices Fabricated with Passivated High-Aluminum III-V Material" can be referred to. The contents of both of these patents are incorporated herein by reference.

In the restricted radiation spot LED shown in FIG. 11, the uppermost layer 24 can be a p-type conductive layer containing aluminum (but is not limited to this). The mesa 33 can be a transparent p-type layer containing aluminum. The volumetric oxidation rate of the top layer 24, or the lateral oxidation rate of the conductive layer, is greater than the volumetric oxidation rate of the upper limiting layer 23 if the particular LED 100 does not have a separate top layer 24. , Select one having a high molar ratio as the composition of the conductive layer (which consists of, for example, a III-V semiconductor having a high aluminum concentration). FIG. 11 shows an LED device with an exposed layer containing aluminum. Anisotropic oxidation of the aluminum-containing layer causes mesa 33 and natural oxide 34 to form. The insulating properties of the natural oxide 34 limit the current to these regions, which results in a restricted emission spot LED. The top layer 24 and the mesa 33, which are p-type conductive layers containing aluminum in this example, can be formed from any transparent compound containing aluminum, which has appropriate anisotropy in the oxidation rate.

12 and 13 show an embodiment of the present invention including two optical elements 28 and 29, one of the two optical elements being coated with a reflective material 40 to form a reflective portion. .. FIG. 12 shows an optical element 29 as a reflecting portion 29 provided on the side opposite to the surface having the Fresnel lens 28. The grooves of both the Fresnel lens 28 and the reflecting portion 29 are patterned so as to collimate the incident light rays. Therefore, when the photon emitted from the light source 27 travels along the path shown by the broken line and hits the reflecting unit 29, the reflecting unit 29 collimates and reflects the photon and returns it in the direction of the upper Fresnel lens 28. Without the reflector 29, the photons emitted from the point light source 27 would travel along the path 5 shown in FIG. 7A and would not exit the light emitting device. Photons along path 5 are repeatedly reflected, absorbed, attenuated, or taken out from a surface that is not the extraction surface.

FIG. 13 shows a Fresnel lens 28 on one surface of the light emitting device and a reflecting portion 29 on the opposite surface, as in FIG. However, the groove of the reflecting portion 29 of FIG. 13 does not collimate the incident photons as shown in FIG. 12, but instead focuses on the point light source 27. The light emitting device of FIG. 13 enhances the intensity of the light taken out along the axis by advancing the photons that would have traveled along the path 6 in FIG. 12 along the path 7 of FIG. The reflecting unit 29 in FIG. 13 collimates and focuses the incident photons toward the Fresnel lens 28 by adjusting the distance δ, the horizontal position of the reflecting unit 29, and one or more of the groove patterns. It can be made to diverge or guide. Similarly, photons can be guided away from absorption areas within the LED, such as the active layer 22, contacts 31 and 32. Those skilled in the art will be able to design Fresnel lenses and tailor the desired radiation pattern to suit a particular application. For example, the example of FIG. 13 is more preferred than the example of FIG. 12 for application purposes that require high strength along the axis.

In the examples shown in FIGS. 14 and 15, the present invention does not require an optical element on the extraction surface. The photons emitted from the point light source 27 are focused in FIG. 14 and diverged in FIG. In either case, the photons are reflected upwards towards the extraction surface. The embodiment of FIG. 14 has high strength along the axis as in the embodiment of FIG. 13, and is useful for an application purpose requiring high strength along the axis, for example, application to an optical fiber.

FIG. 16 shows a light emitting device using a flip chip structure. In the flip-chip structure, the contacts 31 and 32 can be arranged on the same side, in this case the bottom side. Since the contacts 31 and 32 often absorb light and occupy a part of the light extraction surface, removing them from the light extraction surface allows more light to be removed from the LED device through the light extraction surface. be able to.

FIG. 17 shows a light emitting device in which the orientations of the sealing layers 21 and 23 and the active layer 22 are substantially perpendicular to the extraction surface. In the light emitting device shown in FIG. 17, the semiconductor light emitting device 100 of FIG. 1 is rotated by 90 degrees so that light is extracted from the side surface of the semiconductor light emitting device 100. Similar to the flip-chip structure, the structure shown in FIG. 17 has the advantage that there are no contacts on the take-out surface.

A large number of LEDs of the present invention can be combined and used for high output applications. For example, FIG. 18 shows three light emitting devices of the type shown in FIG. 13 arranged in an array so as to emit high light output. These diode arrays, which can be formed on an LED chip or on a wafer, typically have a larger area than a chip of a single semiconductor light emitting device. Further, the LED device of the present invention is suitable for a color display panel using red, green, and blue LEDs as pixel elements. Such displays are well known and an example of this is shown in FIG. The display panel 50 includes red (52), green (54), and blue (56) LEDs, respectively, and has an array of light emitting devices that display images by selectively illuminating them by a well-known circuit. .. In FIG. 19, only three pixels are shown for simplicity. As one example, the light emitting device was arranged in a column shape. As another embodiment, the light emitting device can be arranged in another pattern, such as a triangle. A light emitting device with a high light extraction rate can also be used for the backlight of an LCD display.

Although the present invention has been illustrated with specific examples, it is not intended to limit the scope of the invention to these specific or preferred examples exemplified. For example, for devices such as photodetectors and solar cells, the examples disclosed herein would be useful.

20 ... Substraight, 21 ... Lower sealing layer, 22 ... Active layer, 23 ... Upper sealing layer, 24 ... Top layer, 26 ... Multilayer structure, 27 ... Light source, 28 ... Fresnel lens, 31, 32 ... Contact, 33 ... Mesa, 34 ... Oxide, 40 ... Reflective material, 70 ... Stamping block, 100 ... Semiconductor light source, 50 ... Display panel, 52 ... Red LED, 54 ... Green LED, 56 ... Blue LED